Production of tri- and perchloroethylenes



United States Patent Ofiice 3,234,296 PRODUCTION OF TEL AND PER- CHLORQETHYLENES Alfred A. DAddieco, Wilmington, Del, and Harry 0. Burrus, Lewiston, and Leslie J. Todd, Grand Island, N.Y., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed June 1, 1962, Ser. No. 199,235 8 Qlaims. (Cl. 250-654) This invention relates to an improved process for the production of chlorinated ethylenes by heating chlorethanes alone or in the presence of chlorine. It is particularly related to an improved process for the preparation of trichlorethylene and perchlorethylene from tetrachlorethane.

Processes for the production of trichlorethylene and/ or perchlorethylene by the pyrolysis of tetrachlorethane alone or in admixture with chlorine always yield high boiling chlorinated by-products. These high boiling materials represent a loss of process raw materials and constitute a difiicult disposal problem since they have a toxic nature and tend to evolve corrosive vapors. Since trichlorethylene and perchlorethylene are manufactured in large commercial quantities even a small percent of these high boiling by-products represents a large quantity of nudesirable waste.

One of the objects of this invention is to provide an improved process for the manufacture of chlorethylenes in which a major proportion of the high boiling byproducts are converted to useful chlorethylenes. Another object is to provide a process for the production of trichlorethylene and perchlorethylene from chlorethanes alone or in admixture with chlorine in which the high boiling chlorinated by-products are converted to chlorethylenes. Further objects will become apparent from the following description.

The above enumerated and further objects of this invention are obtained principally in the production of trichlorethylene and perchlorethylene by the gas-phase pyrolysis of a partially chlorinated ethane raw material, containing at least 50% by Weight of tetrachlorethane, alone or in the presence of chlorine, in which hexachlorethane obtained by the chlorination of the high boiling byproducts of the pyrolysis are combined With the chlorethane raw material. This process involves a combination of the following steps:

(1) The chlorethane raw material or process feed mixture is adjusted to contain from at least 1%, or preferably 5%, by weight of hexachlorethane to an amount equivalent to less than one mole of hexachlorethane or one mole of hexachlorethane plus chlorine, if chlorine is combined therewith, for each mole of tetrachlorethane in the feed mixture.

(2.) A high boiling by-product of the pyrolysis process is isolated by distilling the crude product thereof so as to obtain a fraction boiling in the range of from about 165 C. to about 250 C.

(3) The high boiling by-product fraction of step (2) is converted to hexachlorethane by reaction with chlorine at an elevated temperature and pressure.

(4) The hexachlorethane obtained in step (3) is combined with tetrachlorethane and other chlorethanes, such as pentachlorethane, recovered from the pyrolysis process, to produce the chlorethane process feed mixture of step A preferred alternate or modification of this process involves the addition of trichlorethylene to the chlorethane process feed mixture in amounts equivalent to up to two moles, or preferably 0.5 to 2 moles, for each mole of hexachlorethane in this mixture. When this is 3,2342%? Patented Feb. 3, 1966 clone the conversion of hexachlorethane to chlorethylene products is appreciably increased. The addition of trichlorethylene is almost essential when the chlorethane feed is pyrolyzed in combination with chlorine since chlorine tends to lower hexachlorethane conversion to an impractical value.

T he process of this invention is especially useful When it is employed in conjunction with the chlorethylene process of Copelin et al., US. Patent 2,957,923 (October 25, 1960). Although the Copelin et al. process gives a relatively low yield of high boiling by-product residue, the process of this invention for converting these products to useful chlorethylenes adds appreciably to the manufacturing economy.

In carrying out the process of this invention, the highboiling byproduct residue from the chlorethylene process is isolated following distillation of trichlorethylene, perchlorethylene, and chlorethanes, such as the unreacted tetrachlorethane and most of the pentachlorethane contained therein. This residue is then subjected to distillation to obtain a high-boiling fraction preferably, one which distills in the range of about 165 to about 240 C., at atmospheric pressure. The high-boiling by-product fraction is then subjected to liquid-phase chlorination preferably at temperatures of about 200 to 300 C. and pressures of about 200 to 300 pounds per square inch gauge (p.s.i.g.). Under these conditions it has been found that the high boiling byproduct fraction is converted to hexachlorethane in a yield of approximately 90% or better. The hexachlorethane from the chlorination step is then added to the feed of the chlorethane pyrolysis process which thus comprises tetrachlorcthane, pentachlorethane and hexachlorethane alone or in combination with chlorine gas in an amount equivalent to not ver a total of one mole per mole of tetrachlorethane. As disclosed in the above-mentioned Copelin et al. patent, the chlorethane pyrolysis step is carried out at a temperature in the range 359 to 525 C. The molar ratio of hexachlorethane plus chlorine, if present, to tetrachlorethane in the feed mixture is less than one. In general, the molar ratio of hexachlorethane to tetrachlorethane in the chlorethane feed is about 0.05 to 0.4. When trichlorethylene is added to the pyrolysis feed gases, up to 0.5 to two molecular proportions are usually added per mole of hexachlorethane. In general, the trichlorethylene constitutes not over 5 to 10% by Weight of the total feed gas. Under the conditions of this invention it has been found that the percent of high boiling byproducts in the crude product does not increase when the pyrolysis is run in a continuous manner and all of the hexachlorethane obtained from the high boiling fraction is recycled.

The composition and amount of the high boiling byproducts obtained in the chlorethane pyrolysis is determined both by the pyrolysis temperature and the composition of the feed with respect to the agents other than tetrachlorethane, e.g., pentachlorethane, hexachlorethane and chlorine. The exact composition of the high boilers is not known although the presence of such constituents as pentachlorobutadiene, hexachlorobutadiene, pentachlorobutene and hexachlorobutane have been demonstrated. The yield of hexachlorethane obtainable from high boilers by chlorination varies. However, with the combination of steps of this invention when carried out in the preferred manner, the yield of hexachlorethane as previously noted is 90% or better and may even be substantially quantitative. The yield of high boiling byproducts other than unconverted hexachlorethane increases with the pyrolysis temperature so that for best results, the process should be carried out under conditions which make it possible to operate with practical yields at the lowest possible pyrolysis temperature. When the process of this invention is employed in conjunction with the chlorethylene process of Copelin et al., US. Patent 2,957,923, the pyrolysis reactor comprises a heated zone and an unheated zone whose relative sizes are such that the exposure of the reaction products to the unheated zone is preferably about ten times that of the heated zone. In this connection, the yield of high boilers other than hexachlorethane per 100 pounds of trichlorethylene plus perchlorethylene has been measured as a function of the temperature of the unheated zone when the heated zone is about 450 C. These values are shown in Table 1.

TABLE 1 Average temperature High boilers excluding of heated zone hexachlorethane (degrees C.): (lbs/100 lbs. triperchlorethylene) The average temperature of the secondary unheated reactor zone is determined by the degree of insulation and the relation of wall area to volume.

The invention may be understood in more detail from the following illustrative examples. It should be understood that these examples should not be construed as limiting the invention.

Example 1 Ina continuous gas-phase pyrolysis of tetrachlorethane, a feed gas mixture of tetrachlorethane, hexachlorethane obtained by the chlorination of high boiling by-products of the pyrolysis reaction, and a small amount of recycled pentachlorethane was passed through a reactor comprising a heated zone and an unheated zone at the rate of approximately 700 parts by weight per hour. The heated zone was maintained at a temperature of 448 C. and the unheated zone had a temperature of 438 C. The relative size of two reaction zones was such that exposure time in the unheated zone was about ten times that in the heated zone. The composition of the chlorethane feed mixture and the crude gaseous product in parts per 100 by weight are shown in the following table.

The results of this example demonstrate that 90% of the hexachlorethane is consumed in the reaction and that the weight of high boiling by-products including unreacted hexachlorethane is relatively low. The net yield of useful chlorethylene products is high since the pentachlorethane in the product can be recycled and at least 90% of the high boilers can be converted to hexachlorethane for recycle.

Example 2 The influence of trichlorethylene on the conversion of added hexachlorethane in the chlorethane pyrolysis process was demonstrated by two experiments substantially similar to Example 1 except that the unheated reactor zone Was at a temperature of about 375 C. In one experiment 8 percent trichlorethylene was added in the feed gas; in the other trichlorethylene was absent. At the temperatures employed in these experiments, the conversion was lower than in Example 1 but the yield of high boiling by-products was considerably reduced. The composition of the feed gas and gaseous product when trichlorethylene was added to the feed are shown in Table 2. These values are in parts per by weight.

TABLE 3 Compounds Chlorethane Product Feed Tetrachlorethane 8O 12 Pentachlorethaue 2 3 Hexachlorethane- 1O 3 'Irichlorethylene- 8 57 Perchlorethylen 9 High boilers 1 Hydrogen chloride 1 15 To determine the effect of chlorine on the conversion of hexachlorethane to chlorethylene products in the tetrachlorethane pyrolysis reaction, a series of tests were carried out similar to Example 1 but with varying percentages of chlorine in the feed gas. In all of these tests the heated reactor zone was kept at about 450 C. and the unheated zone was about 400 C. Table 4 shows the variation of hexachlorethane conversion with variation of the weight percent of chlorine in the feed gases.

TABLE 4 Chlorine in feed gas: Hexachlorethane converted 0.0 81 5.6 51 8.8 39 12.9 19

Example 4 The influence of trichlorethylene on the conversion of added hexachlorethane in the tetrachlorethane pyrolysis reaction when chlorine is present is illustrated by two tests substantially similar to Example 1 in which the heated reactor zone was at 455 C. and the unheated zone was at 377 C. In both of these tests the feed gas contained 7% by weight of chlorine. However, in the first test, 4A, only 1% trichlorethylene was present in the feed gases whereas 7% was present in the second test, 4B. The composition of feed gas including chlorine and product in parts per 100 by weight is shown for both of these tests in Table 4.

In Test 4A, the hexachlorethane conversion is only whereas in Test 413 in which the feed gas contains 7% trichlorethylene, the hexachlorethane conversion is 44%.

The embodiments of the invention in which an exclusive property or privilege is claimed are as follows:

1. In a process for the production of trichlorethylene and perchlorethylene by the gas-phase pyrolysis of a chiorethane feed mixture containing at least 50% by weight of tetrachlorethane at a temperature in the range of 350 525 C. the improvement comprising, in combination, the steps:

(a) employing in the gas-phase pyrolysis step a chlorethane feed mixture containing at least 1% by Weight of hexachlorethane in which the mole ratio of hexachlorethane to tetrachlorethane is less than one,

(b) separating a high boiling by-product by distilling the crude chloroethylene product of said pyrolysis to obtain a fraction boiling in the range of about 165 to about 250 C.,

(c) reacting the said by-product fraction with chlorine in the liquid phase at an elevated temperature of about 200 to about 300 C. and a pressure of about 200 to about 300 p.s.i.g. to produce hexachlorethane, and

(d) combining hexachlorethane obtained in the byproduct chlorination of step (c) with tetrachlorethane to obtain the chlorethane feed mixture of step (a).

2. The process of claim 1 wherein up to two moles of trichlorethylene are added to the chlorethane feed mixture for each mole of hexachlorethane.

3. In a process for the production of trichlorethylene and perchlorethylene by the gas-phase pyrolysis of a chlorethane feed mixture containing at least 50% by weight of tetrachlorethane at a temperature in the range of SSW-525 C. the improvement comprising, in combination, the steps:

(a) employing in the gas-phase pyrolysis step a chlorethane feed mixture containing at least 1% by weight of hexachlorethane in combination with chlorine in such proportion that the mole ratio of hexachlorethane plus chlorine to tetrachlorethane is less than one,

(b) separating a high boiling by-product by distilling the crude chloroethylene product of said pyrolysis to obtain a fraction boiling in the range of about 165 to about 250 C.,

(c) reacting the said by-procluct fraction with chlorine in the liquid phase at an elevated temperature of about 200 to about 300 C. and a pressure of about 200 to about 300 p.s.i.g. to produce hexachlorethane, and

(d) combining hexachlorethane obtained in the byproduct chlorination of step (c) with tetrachlorethane to obtain the chlorethane feed mixture-chlorine combination of step (a).

4. The process of claim 3 wherein up to two moles of trichlorethylene are added to the chlorethane feed mixture for each mole of hexachlorethane.

5. In a process for the production of trichlorethylene and perchlorethylene by the gas-phase pyrolysis of a 6 chlorethane feed mixture containing at least 50% by weight of tetrachlorethane at a temperature in the range of 350-525 C. the improvement comprising, in combination, the steps:

(a) employing in the gas-phase pyrolysis step a chlorethane feed mixture containing at least about 5% by weight of hexachlorethane in which the mole ratio of hexachlorethane to tetrachlorethane is less than 0.4,

(b) separating a high boiling byproduct by distilling the crude chlorethylene product of said pyrolysis to obtain a fraction boiling in the range of about to about 250 C.,

(c) reacting the said by-product fraction with chlorine at a temperature of about 200 to about 300 C. and about 200 to about 300 pounds p.s.i.g. to produce hexachlorethane, and

(d) combining hexachlorethane obtained in the byproduct chlorination step (c) with tetrachlorethane to obtain the chlorcthane feed mixture of step (a).

6. The process of claim 5 wherein 0.5 to two moles of trichlorethylene are added to the chlorethane feed for each mole of hexachlorethane.

7. In a process for the production of trichlorethylene and perchlorethylene by the gas-phase pyrolysis of a chlorethane feed mixture containing at least 50% by weight of tetrachlorethane at a temperature in the range of 350525 C. the improvement comprising, in combination, the steps:

(a) employing in the gas-phase pyrolysis step a chlorethane feed mixture containing at least 5% by weight of hexachlorethane in combination with chlorine in such proportion that the mole ratio of hexachlorethane plus chlorine to tetrachlorethane is less than one,

(b) separating a high boiling byaproduct by distilling the crude chlorethylene product of said pyrolysis to obtain a fraction boiling in the range from about 165 to about 250 C.,

(c) reacting the said by-product fraction with chlorine at a temperature of about 200 to about 300 C. and about 200 to about 300 p.s.i.g. to produce hexachlorethane, and

(d) combining hexachlorethane obtained in the byproduct chlorination of step (c) with tetrachlorethane to obtain the chlorethane feed mixture-chlorine combination of step a).

8. The process of claim '7 wherein 0.5 to two moles of trichlorethylene are added to the chlorethane feed for each mole of hexachlorethane.

References Cited by the Examiner UNlTED STATES PATENTS 2,178,622 11/1939 Basel et a1. 2,957,923 10/1960 Copelin et a1. 260-654 OTHER REFERENCES McBee et al., Ind. Eng. Chem, vol. 35, pages 317- 320 (1943).

LEON ZITVER, Primary Examiner. 

1. IN A PROCESS FOR THE PRODUCTION OF TRICHLORETHYLEEN AND PERCHLORETHYLENE BY THE GAS-PHASE PYROLYSIS OF A CHLORETHANE FEED MIXTURE CONTAINING AT LEAST 50% BY WEIGHT OF TETRACHLORETHANE AT A TEMPERATURE IN THE RANGE OF 350*525*C. THE IMPROVEMENT COMPRISING, IN COMBINATION, THE STEPS: (A) EMPLOYING IN THE GAS-PHASE PYROLYSIS STEP A CHLORETHANE FEED MIXTURE CONTAINING AT LEAST 1% BY WEIGHT OF HEXACHLORETHANE IN WHCIH THE MOLE RATIO OF HEXCHLORETHANE TO TETRACHLORETHANE IS LESS THAN ONE, (B) SEPARATING A HIGH BOILING BY-PRODUCT BY DISTILLING THE CRUDE CHLOROETHYLENE PRODUCT OF SAID PYROLYSIS TO OBTAIN A FRACTION BOILING IN THE RANGE OF ABOUT 165* TO ABOUT 250*C., (C) REACTING THE SAID BY-PRODUCT FRACTION WITH CHLORINE IN THE LIQUID PHASE AT AN ELEVATED TEMPERATURE OF ABOUT 200* TO ABOUT 300*C. AND A APRESSURE OF ABOUT 200 TO ABOUT 300 P.S.I.G. TO PRODUCE HEXACHLORETHANE, AND (D) COMNBINING HEXACHLORETHANE OBTAINED IN THE BYPRODUCT CHLORINATION OF STEP (C) WITH TETRACHLORETHANE TO OBTAIN THE CHLORETHANE FEED MIXTURE OF STEP (A). 